Telemetric devices are used for remote measuring and transmitting data, such as measurement information, to a central control unit. Exemplary applications of telemetry are automatic meter reading, patient monitoring, traffic monitoring and control, remote weather stations, resource distribution monitoring.
Typically a telemetric device communicates with the central control unit via a radio interface. GPRS is a technology that may be used for data communication between the telemetric device and the central control unit. GPRS and its third and fourth generation evolution is nowadays considered the leading standard for wireless data communication, making this technology the preferred choice for many system vendors and operators. GPRS is specified for example in 3rd Partnership Project (3GPP) Technical Specification 23.060 version 7.5.0 and in 3GPP TS 44.065, version 7.0.0.
In order to enable a telemetric device to connect to a GPRS network, it must be equipped with GPRS communication capability, i.e. a subscriber identity module (SIM) card and a radio unit for wireless connection. Furthermore the telemetric device must be provided with a subscription with the GPRS network operator. The telemetric device behaves like a normal GPRS subscriber, i.e. it attaches to the GPRS network and establishes a Packet Data Protocol (PDP) context for data communication. A PDP context describes the characteristics of a data session between a device and the GPRS network. It refers to a data record comprising session information for an active GPRS session, for the purpose of exchanging data between said device and a service or application in the internet. The GPRS attach procedure is executed whenever a GPRS enabled device is switched on and needs to inform the network about its presence and capabilities. The GPRS attach procedure is initiated by the device and involves signaling between the device and nodes in a GPRS network, such as the serving GPRS support node (SGSN), home location register (HLR) and equipment identity register (EIR). The GPRS attach procedure constitutes exchange of messages for authentication of the device and the subscription, indicating supported ciphering algorithms and other capabilities of the device, and for performing a location update of the device.
According to the state of the art each telemetric device is treated as an individual GPRS subscriber. Each of the corresponding subscriptions is stored and maintained in a subscriber database, such as the Home Location Register (HLR). The number of telemetric devices having a GPRS subscription is rapidly growing and so is the number of data transmissions over the GPRS network per telemetric device. Hence, the signaling resulting from the GPRS attach procedure that is executed for each telemetric device puts a high load on the network. Another disadvantage is that the significant increase of the number of subscriptions required for the telemetric devices overloads the resources of the HLR.